Adjustable booster seat



FIG. 1 is a perspective view of an adjustable booster seat showing my new design;

FIG. 2 is a top view thereof;

FIG. 3 is a bottom view thereof;

FIG. 4 is a left-side view thereof;

FIG. 5 is a right-side view thereof;

FIG. 6 is a back view thereof;

FIG. 7 is a front view thereof; and

FIG. 8 is a perspective view of an alternate embodiment thereof. 

The ornamental design for an adjustable booster seat, substantially as shown and described. 